This invention relates to an optoelectronic bistable apparatus.
More advanced development of optoelectronic devices and elements which include semiconductor lasers and light-emitting diodes is expected to lead to new production of photocomputers and photoexchangers. In particular the optoelectronic bistable unit is attracting enthusiastic research and development. An optoelectronic bistable apparatus has certain indispensable properties. First, the apparatus should have an element structure which ensures planar light emission in order to enable, for example, a photocomputer to carry out the parallel processing of optical signals in as small an area as possible. Second, the apparatus should have a light-amplifying function so as to permit connection of the elements in series; and thirdly that the apparatus should manifest a quick response capability.
Conventional bistable elements are described in "Dynamic Switch Logic--A New Concept for Digital Optical Logic Using DOES Devices", IEDM 85, pp 654-657 by G. W. Taylor et al., and "A new double heterostructure optoelectronic switching device using molecular beam epitaxy", J. Appl. Phys. 59(2), 15, January 1986, pp. 596-600 by the same authors. These proposed bistable elements are of the planar light-emitting type, and are characterized in that parallel processing can be easily carried out; they have a light-amplifying function, thus practically satisfying the fundamental requirements; further they are provided with an auxiliary electrode which achieves a high degree of element control.
However, the aforementioned elements still leave many problems unsolved. One of the problems accompanying the proposed devices is that since the light-emitting n type GaAs layer directly contacts an extremely thin p.sup.+ type GaAs layer of a high impurity concentration, the interface property of the n type GaAs layer is deteriorated. As a result, non-light-emitting recombination frequently takes place in an interface between the n type GaAs layer and the p.sup.+ type GaAs layer. This undesirable recombination obstructs the elevation of a light-emitting property.
Another problem with the aforesaid devices regards the placing of an auxiliary electrode. The auxiliary electrode is provided to control the height of a potential barrier prepared from an extremely thin p.sup.+ type GaAs layer. Fundamentally, therefore, it is preferred that the auxiliary electrode be directly ohmic-contacted to the p.sup.+ type GaAs layer. Since, however, the p.sup.+ type GaAs layer is extremely thin, it is impossible to mount auxiliary on the p.sup.+ type GaAs layer. Unavoidably, therefore, the auxiliary electrode is mounted on the light-emitting n type GaAs layer. Consequently the aforementioned bistable devices fail to exhibit quick response characteristics because of the above-mentioned undesirable location of the auxiliary electrode.